A prior observational study indicated an asymmetric link between sea surface temperature(SST)in the Tasman Sea and ENSO during austral summer.Specifically,El Niño is associated with a dipolar SST anomaly pattern,...A prior observational study indicated an asymmetric link between sea surface temperature(SST)in the Tasman Sea and ENSO during austral summer.Specifically,El Niño is associated with a dipolar SST anomaly pattern,featuring warming in the northwest and cooling in the southeast,whereas La Niña corresponds to basin-scale warming.This study employs the experiments of coupled models from the sixth phase of the Coupled Model Intercomparison Project(CMIP6)to assess ENSO’s impact on Tasman Sea SST.While all 15 models capture the observed dipolar SST anomalies(SSTAs)in the Tasman Sea during El Niño years,only 7 models capture the basin-scale warmth in the Tasman Sea during La Niña years.Consequently,the models are bifurcated into two groups:group-one models yield one physically reasonable asymmetric connection as observed,including the asymmetry of oceanic heat transport,especially the Ekman meridional transport anomalies induced by zonal wind stress driven by the asymmetric atmospheric circulation over the Tasman Sea.However,due to abnormal responses to ENSO and systematic biases in model simulations,including jet and storm tracks,oceanic heat fluxes,ocean currents,and SST,the group-two models fail to reproduce the asymmetric connection between the Tasman Sea and ENSO.This study not only validates the observational asymmetric connection of SSTAs in the Tasman Sea with respect to the two opposite ENSO phases,but also provides evidence and clues to reduce the bias in group-two models.展开更多
Sea surface temperature(SST)is an important ocean variable affecting climate change.It plays an important role in the interactions between the ocean and the atmosphere,and it also has an effect on the transport of hea...Sea surface temperature(SST)is an important ocean variable affecting climate change.It plays an important role in the interactions between the ocean and the atmosphere,and it also has an effect on the transport of heat,freshwater,and carbon.Therefore,accurate SST prediction is necessary for understanding climate change and protecting ocean ecosystems.In this study,we proposed a hybrid model to predict SST in the tropical Pacific Ocean based on two single deep-learning models.Results indicate that the proposed hybrid model shows superior prediction accuracy at all lead times compared to the single model.Specifically,during El Niño periods,the root mean square error,mean absolute error,and Pearson correlation coefficient of the hybrid model forecasts were approximately 0.54℃,0.40℃,and 0.98,respectively,while during La Niña periods,these metrics were 0.55℃,0.39℃,and 0.98,respectively.Notably,the hybrid model was able to capture the spatial distribution of SSTs during the El Niño-Southern Oscillation(ENSO)events more accurately relative to a single model.Moreover,the prediction results of the hybrid model in different ocean regions exhibited lower prediction errors and higher correlations.The ablation experiments showed that sea surface wind(SSW)had different effects on SST at different times.By combining SST and SSW data,the model can make more-accurate predictions under different climatic conditions.The proposed hybrid model is able to predict SSTs quickly and accurately with better robustness during ENSO.展开更多
In this study,thermo-fluid characteristics of elliptical annular finned tube heat exchanger were numerically studied in detail.Transition SST model was utilized to simulate turbulent flow.Effects of air velocities,hor...In this study,thermo-fluid characteristics of elliptical annular finned tube heat exchanger were numerically studied in detail.Transition SST model was utilized to simulate turbulent flow.Effects of air velocities,horizontal to vertical fin diameter ratios,and fin densities were examined in detail.The simulations indicate superior performance of elliptical fin layout.It was shown that pressure drop of annular elliptical fin can be only one half of that of a circular annular fin while containing comparable heat transfer performance.The vertical elliptical annular fin may even contain a higher heat transfer performance over circular fin.Correlations are proposed to estimate the Nu number and pressure drop based on the annular circular fin.The maximum deviations between the proposed correlations and simulations regarding pressure drop and heat transfer coefficient are 5.6%and 3.2%,respectively.For further elaboration of the superiority of the elliptical layout from the second law perspective,normalized entropy generation was also studied.In all cases,the entropy generation rate in circular fin was higher than that of an elliptical fin.展开更多
-Starting from physical oceanology characteristics of the China seas and for the short-term operational prediction of SST in the region, a two-dimensional (vertically integrated) primitive equation model, physically r...-Starting from physical oceanology characteristics of the China seas and for the short-term operational prediction of SST in the region, a two-dimensional (vertically integrated) primitive equation model, physically reasonable and operationally feasible,on the upper mixed layer is constructed and given here, which consists of three parts, the nondivergent residual current (the monthly mean field of the Kuroshio and its branches) equations, the dynamic forecasting equations, and the equation of model's physics consisting of surface heat flux, coolings of the upper mixed layer due to the Ekman pumping and the entrainment by gale. This model may be used primarily to forecast the sea surface temperature, and to give estimations of the mean wind-driven current and the sea level, for a period of 3-5 d. In part 1 of this series, the physical conditions for establishing model equations are discussed first, that is, 1. the existence of the upper well mixed layer in the region; 2. the distinguishability of currents of all kinds; 3. the splitting of thermodynamical equation. The equations of nondivergent residual current, and the dynamic forecasting equations with initial values and boundary conditions are also discussed.展开更多
Based on the historical and RCP8.5 runs of the multi-model ensemble of 32 models participating in CMIP5, the present study evaluates the formation mechanisms for the patterns of changes in equatorial Pacific SST under...Based on the historical and RCP8.5 runs of the multi-model ensemble of 32 models participating in CMIP5, the present study evaluates the formation mechanisms for the patterns of changes in equatorial Pacific SST under global warming. Two features with complex formation processes, the zonal E1 Nifio-like pattern and the meridional equatorial peak warm- ing （EPW）, are investigated. The climatological evaporation is the main contributor to the E1 Nifio-like pattern, while the ocean dynamical thermostat effect plays a comparable negative role. The cloud-shortwave-radiation-SST feedback and the weakened Walker circulation play a small positive role in the E1 Nifio-like pattern. The processes associated with ocean dynamics are confined to the equator. The climatological evaporation is also the dominant contributor to the EPW pattern, as suggested in previous studies. However, the effects of some processes are inconsistent with previous studies. For example, changes in the zonal heat advection due to the weakened Walker circulation have a remarkable positive contribution to the EPW pattern, and changes in the shortwave radiation play a negative role in the EPW pattern.展开更多
Solid state transformer(SST)can provide more advanced functionalities compared with conventional transformer,and has great potential in smart grid application.Recently,the SST with medium frequency(MF)isolation link a...Solid state transformer(SST)can provide more advanced functionalities compared with conventional transformer,and has great potential in smart grid application.Recently,the SST with medium frequency(MF)isolation link and magnetic integration feature has been proposed,which can reduce the system volume and thus increase the power density.However,the magnetic integration also introduces strong coupling between the line frequency(LF)and MF variables,which poses a great challenge on modeling and control issues.This paper proposes a modeling and control method for an SST with magnetic integration and mixed-frequency modulation.A mathematical model based on dual d-q references is deduced,and then a cascaded control system is designed according to the model.Parameters of the controller for the variables at one frequency are properly designed to avoid disturbance from the variables at the other frequency.The simulation and experimental results show good decoupling effect and satisfactory dynamics performance of the proposed control system.展开更多
-The model's physical equation is used to parameterize some subgrid-scale processes and physical processes in the present numerical model. The transmission and attenuation of the solar energy in the ocean are cons...-The model's physical equation is used to parameterize some subgrid-scale processes and physical processes in the present numerical model. The transmission and attenuation of the solar energy in the ocean are considered. A simple diagnostic equation for the cloud fractions k proposed on the basis of the humidities at the surface and the mid-troposphere. The parameterized formulae of both entrainment and Ekman pumping are improved.In the numerical integration, the treatment on damping the inertial oscillations is emphasized. The initialization and the objective analysis of the data which are necessary for the operational prediction will be presented in another paper.Results of SST prediction and some numerical experiments are given here. The model is computationally stable and successful in modelling the behaviors of the drift current and the mixed layer physics, and the AMD (absolute mean deviations) ≤1. 2℃ , RC (correlation coefficients ) ≥85% for 3-day forecasting.展开更多
RANS是工程中常用的CFD数值模拟模型,文中基于该模型对SUBOFF裸艇体的水动力特性开展数值模拟研究.传统SST(shear stress transport model)湍流模型采用了线性涡黏假设,难以描述复杂流场的各向异性流动现象.另外,传统SST模型对分离点的...RANS是工程中常用的CFD数值模拟模型,文中基于该模型对SUBOFF裸艇体的水动力特性开展数值模拟研究.传统SST(shear stress transport model)湍流模型采用了线性涡黏假设,难以描述复杂流场的各向异性流动现象.另外,传统SST模型对分离点的预测还可能出现延迟,使阻力预测值偏小.针对传统SST湍流模型的缺陷,提出使用各向异性的ASST(anisotropic shear stress transport)湍流模型及其再附修正来研究SUBOFF裸艇体的数值模拟计算问题,并对SST、SST(Reattach)、ASST及ASST(Reattach)4种湍流模型进行了比较研究.结果表明,相较于传统SST模型,ASST模型在预测SUBOFF裸艇的阻力上具有更高精确度,再附修正可有效克服阻力预测值偏小的问题,ASST(Reattach)模型在4种湍流模型中阻力预报性能最优.另外,针对不同站位的轴向及径向平均速度分布特性问题,4种湍流模型均能够取得与模型试验一致的数值模拟结果.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2023YFF0805101)the National Natural Science Founda-tion of China(Grant Nos.42376250 and 42405068).
文摘A prior observational study indicated an asymmetric link between sea surface temperature(SST)in the Tasman Sea and ENSO during austral summer.Specifically,El Niño is associated with a dipolar SST anomaly pattern,featuring warming in the northwest and cooling in the southeast,whereas La Niña corresponds to basin-scale warming.This study employs the experiments of coupled models from the sixth phase of the Coupled Model Intercomparison Project(CMIP6)to assess ENSO’s impact on Tasman Sea SST.While all 15 models capture the observed dipolar SST anomalies(SSTAs)in the Tasman Sea during El Niño years,only 7 models capture the basin-scale warmth in the Tasman Sea during La Niña years.Consequently,the models are bifurcated into two groups:group-one models yield one physically reasonable asymmetric connection as observed,including the asymmetry of oceanic heat transport,especially the Ekman meridional transport anomalies induced by zonal wind stress driven by the asymmetric atmospheric circulation over the Tasman Sea.However,due to abnormal responses to ENSO and systematic biases in model simulations,including jet and storm tracks,oceanic heat fluxes,ocean currents,and SST,the group-two models fail to reproduce the asymmetric connection between the Tasman Sea and ENSO.This study not only validates the observational asymmetric connection of SSTAs in the Tasman Sea with respect to the two opposite ENSO phases,but also provides evidence and clues to reduce the bias in group-two models.
基金Supported by the National Natural Science Foundation of China(Nos.42476024,42176010)the National Key Research and Development Program of China(No.2022YFF0801400)。
文摘Sea surface temperature(SST)is an important ocean variable affecting climate change.It plays an important role in the interactions between the ocean and the atmosphere,and it also has an effect on the transport of heat,freshwater,and carbon.Therefore,accurate SST prediction is necessary for understanding climate change and protecting ocean ecosystems.In this study,we proposed a hybrid model to predict SST in the tropical Pacific Ocean based on two single deep-learning models.Results indicate that the proposed hybrid model shows superior prediction accuracy at all lead times compared to the single model.Specifically,during El Niño periods,the root mean square error,mean absolute error,and Pearson correlation coefficient of the hybrid model forecasts were approximately 0.54℃,0.40℃,and 0.98,respectively,while during La Niña periods,these metrics were 0.55℃,0.39℃,and 0.98,respectively.Notably,the hybrid model was able to capture the spatial distribution of SSTs during the El Niño-Southern Oscillation(ENSO)events more accurately relative to a single model.Moreover,the prediction results of the hybrid model in different ocean regions exhibited lower prediction errors and higher correlations.The ablation experiments showed that sea surface wind(SSW)had different effects on SST at different times.By combining SST and SSW data,the model can make more-accurate predictions under different climatic conditions.The proposed hybrid model is able to predict SSTs quickly and accurately with better robustness during ENSO.
文摘In this study,thermo-fluid characteristics of elliptical annular finned tube heat exchanger were numerically studied in detail.Transition SST model was utilized to simulate turbulent flow.Effects of air velocities,horizontal to vertical fin diameter ratios,and fin densities were examined in detail.The simulations indicate superior performance of elliptical fin layout.It was shown that pressure drop of annular elliptical fin can be only one half of that of a circular annular fin while containing comparable heat transfer performance.The vertical elliptical annular fin may even contain a higher heat transfer performance over circular fin.Correlations are proposed to estimate the Nu number and pressure drop based on the annular circular fin.The maximum deviations between the proposed correlations and simulations regarding pressure drop and heat transfer coefficient are 5.6%and 3.2%,respectively.For further elaboration of the superiority of the elliptical layout from the second law perspective,normalized entropy generation was also studied.In all cases,the entropy generation rate in circular fin was higher than that of an elliptical fin.
文摘-Starting from physical oceanology characteristics of the China seas and for the short-term operational prediction of SST in the region, a two-dimensional (vertically integrated) primitive equation model, physically reasonable and operationally feasible,on the upper mixed layer is constructed and given here, which consists of three parts, the nondivergent residual current (the monthly mean field of the Kuroshio and its branches) equations, the dynamic forecasting equations, and the equation of model's physics consisting of surface heat flux, coolings of the upper mixed layer due to the Ekman pumping and the entrainment by gale. This model may be used primarily to forecast the sea surface temperature, and to give estimations of the mean wind-driven current and the sea level, for a period of 3-5 d. In part 1 of this series, the physical conditions for establishing model equations are discussed first, that is, 1. the existence of the upper well mixed layer in the region; 2. the distinguishability of currents of all kinds; 3. the splitting of thermodynamical equation. The equations of nondivergent residual current, and the dynamic forecasting equations with initial values and boundary conditions are also discussed.
基金supported by the National Basic Research Program of China (Grant Nos. 2014CB953903 and 2012CB955604)the National Natural Science Foundation of China (Grant Nos. 41575088 and 41461164005)
文摘Based on the historical and RCP8.5 runs of the multi-model ensemble of 32 models participating in CMIP5, the present study evaluates the formation mechanisms for the patterns of changes in equatorial Pacific SST under global warming. Two features with complex formation processes, the zonal E1 Nifio-like pattern and the meridional equatorial peak warm- ing （EPW）, are investigated. The climatological evaporation is the main contributor to the E1 Nifio-like pattern, while the ocean dynamical thermostat effect plays a comparable negative role. The cloud-shortwave-radiation-SST feedback and the weakened Walker circulation play a small positive role in the E1 Nifio-like pattern. The processes associated with ocean dynamics are confined to the equator. The climatological evaporation is also the dominant contributor to the EPW pattern, as suggested in previous studies. However, the effects of some processes are inconsistent with previous studies. For example, changes in the zonal heat advection due to the weakened Walker circulation have a remarkable positive contribution to the EPW pattern, and changes in the shortwave radiation play a negative role in the EPW pattern.
基金the National Natural Science Foundation of China under Grant 51777085.
文摘Solid state transformer(SST)can provide more advanced functionalities compared with conventional transformer,and has great potential in smart grid application.Recently,the SST with medium frequency(MF)isolation link and magnetic integration feature has been proposed,which can reduce the system volume and thus increase the power density.However,the magnetic integration also introduces strong coupling between the line frequency(LF)and MF variables,which poses a great challenge on modeling and control issues.This paper proposes a modeling and control method for an SST with magnetic integration and mixed-frequency modulation.A mathematical model based on dual d-q references is deduced,and then a cascaded control system is designed according to the model.Parameters of the controller for the variables at one frequency are properly designed to avoid disturbance from the variables at the other frequency.The simulation and experimental results show good decoupling effect and satisfactory dynamics performance of the proposed control system.
文摘-The model's physical equation is used to parameterize some subgrid-scale processes and physical processes in the present numerical model. The transmission and attenuation of the solar energy in the ocean are considered. A simple diagnostic equation for the cloud fractions k proposed on the basis of the humidities at the surface and the mid-troposphere. The parameterized formulae of both entrainment and Ekman pumping are improved.In the numerical integration, the treatment on damping the inertial oscillations is emphasized. The initialization and the objective analysis of the data which are necessary for the operational prediction will be presented in another paper.Results of SST prediction and some numerical experiments are given here. The model is computationally stable and successful in modelling the behaviors of the drift current and the mixed layer physics, and the AMD (absolute mean deviations) ≤1. 2℃ , RC (correlation coefficients ) ≥85% for 3-day forecasting.
